Fabrication of most micro- and nano-fabricated devices including semiconductors, photonic and optoelectronic devices, MEMS/NEMS, electronic displays (such as LCDs), etc. requires the deposition of many thin films. Several deposition options exist in the industry today. Deposition in the liquid phase is typically carried out by processes, such as spin-coating, which is often used as a precursor to subsequent reactions that solidify the liquid to obtain the desired thin film. In the vapor phase, the most commonly used technique is that of Chemical Vapor Deposition (CVD). In a typical CVD process, the substrate is exposed to precursors in the gaseous phase that react or decompose to form the desired film on the surface of the substrate. There are several types of CVD processes. Depending upon the pressure used, they can be classified as Atmospheric Pressure CVD (APCVD), Low Pressure CVD (LPCVD) or Ultrahigh Vacuum CVD (UHVCVD). Low pressures tend to reduce unwanted reactions and improve film thickness uniformity. Plasma based methods, such as Plasma Enhanced CVD (PECVD), are used to enhance the chemical reactions. Remote PECVD is also used in the deposition of thin films in the semiconductor industry to lower deposition temperatures and protect the substrate from high-temperature effects. A technique called Atomic Layer Deposition (ALD) is also frequently used to produce conformal monolayers of one or more different materials. Physical Vapor Deposition (PVD) methods are also important thin film deposition techniques. As the name suggests, they do not rely on chemical reactions, but deposit condensed forms of a vaporized material onto the substrate in a vacuum environment. Evaporative deposition and sputtering are two common examples of PVD. The former heats the material to be deposited to a high vapor pressure, while the latter utilizes a plasma discharge to bombard the substrate surface with atoms of the material to be deposited.
All the processes discussed above deposit thin films in a manner where the amount of material deposited per unit area is substantially the same. The ability to tailor materials to form intentionally non-uniform films is not typically possible for these processes. Also, processes, such as spin-coating, involve significant material wastage while vacuum processes can be expensive due to the need to pump down chambers where processing is performed.
Hence, there is not currently a means for forming intentionally non-uniform films without significant material wastage in an inexpensive manner.